I’ve always considered a bug as an actual error/mistake in the coding itself. As far as I am aware everything is working as Indinera intended, both the event to double Wendala’s ST and the formula for the other major ST training event. By comparison, I would consider the mushroom in Gaes Cave that used to increase Sarah’s speed by 1000 if you fail to retrieve it; a bug. It was most likely supposed to check that Sarah has 1000 Speed to succeed, not give her 1000 speed upon failure. Just as a technicality.
That’s just me though; I’d otherwise agree that Wendala’s ST can get completely out of hand. I’d be fine if the bonus capped at 300ST, or just was 300ST to match the magic increase she can take instead. The other training event likewise could have been capped off at maybe 50, 80 or 100ST.
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If you do replay the entire franchise, Laxius Soul 2 might be out by the time you finish Laxius Soul 1!

Enjoy the new walkthrough if you do, and make sure to high five Kratin in LF2 on your way through.